1. Field of the Invention
This invention concerns a new temperature compensation method for semiconductor wafers in rapid thermal processor. Its usage is simple and inexpensive. It also effectively changes the problem of uneven temperature distribution of the rapid thermal processor.
2. Cross-Reference to Related Applications
With advancement in electronics, the size of semiconductors is keep on going shrinking. The development of the technique in nano-meter-size components in ULSI (Ultra Large Scaled Integrated circuit) requires the progress of thickness of the oxygenated gate in the MOSFET towards 50 Angstrom. If the traditional high-temperature thermal growth method is used, a high quality in super-thin oxygenated layer is not possible. In order to obtain a high quality super-thin oxygenated layer, the key technique is to use Rapid Thermal Processing(RTP).
The traditional rapid thermal processing has the heating applied from a set of parallel halogen tube heating lights at the top of the system. Each light tube heats the wafer at the same heating output. It is a single sided heating system. However, the uneven temperature is the crucial problem faced by the traditional rapid thermal processors. The cause of the problem of uneven temperature is due to the following factors:
1. There are more radiation emitted by the surroundings of the wafers. PA1 2. The inter-flow of cold air in the rapid thermal processing system keeps the surrounding of the wafer at a low temperatures. PA1 3. The position of the halogen tube heating lights causes the central portion of the wafers to receive more light than the rim of the wafers.
Therefore, the temperature at the center of the wafer is higher than its rim. The difference is as much as 40% in actual cases.
3. Description of the Prior Art
In order to overcome the above problem, in 1989 R. Singh edited the International Society for Optical Engineering. In its 41.sup.st page it raised a simple temperature compensation method. It utilize a large a silicon ring(larger than the wafer) to absorb the energy of the light in order to compensate for the temperature at the margin of the wafer. However, this sort of compensation could only be to a certain extent. The temperature at the center is still 15% greater than the margin of the wafer. B. J. Cho in the 1994 IEEE Trans. On Semicond. Manuf., 7th document 3rd issue at page 345 raised the issue of the specially designed optical geometric reflection so that the margin of the wafer could be heated by the reflected light. This solves the problem of uneven distribution of temperature. However, the geometric reflection designed for a certain temperature may not be suited for other temperature operations. B-J Cho and the rest, in 1995 K. C. Saraswat in Mat. Res. Symp. Proc. 387th issue at page 35 also raised the issue of adjustment of the position of the ultraviolet light and the active output of the light tube as a solution to the problem of uneven temperature of the wafer. But this method is comparatively more expensive and complicated. In addition, this method requires the entire alteration of the system of rapid thermal processor. The old system will be obsolete and this is a waste to those who owns the old systems. Other than this, according to P. Y. Wong and others in Mat. Res. Symp. Proc. 387th issue at page 15, if the surface of the chip has other material patterns carved on it, then the wafer itself, despite being placed in a rapid thermal processing system of even-temperature, will have uneven surface temperatures. There is no solution yet as to the uneven temperature caused by patterns on wafer surfaces.
Therefore, in order to more effectively solve the problem of uneven temperature of traditional rapid thermal processor, every rapid thermal processor should improve on the problem of the uneven temperature caused by the Pattern, in order to achieve their greatest capacity. The inventors of this invention used their unique knowledge on traditional rapid thermal processors and their professional knowledge on thermal conductivity to invent this simple, economic and effective solution of temperature compensation after continued laboratory experiment.